1. Field of the Invention
The present invention generally relates to a driving apparatus and a method of reducing the spike current thereof, and more particularly, to a driving apparatus applied to an liquid crystal display system (LCD system) and a method of reducing the spike current thereof.
2. Description of Related Art
An LCD system includes a driving apparatus for converting an input signal into an analog driving signal so as make the LCD system display an image specified by the input signal. However, a conventional driving apparatus applied to an LCD system would produce a huge spike current at a conductive moment, which may damage the chips and the panel of the LCD system due to the huge spike current.
FIG. 1 is a circuit diagram of a conventional LCD system 100. Referring to FIG. 1, an LCD system 100 includes a row decoder 101, a column decoder 102 and a plurality of panel units 103, wherein the panel unit 103 is electrically coupled with the row decoder 101 and the column decoder 102. The column decoder 102 is used for outputting a switching signal so as to start up the panel unit 103; the row decoder 101 has a plurality of driving circuits, and the row decoder 101 converts an input signal into an analog driving signal through the driving circuit and outputs the analog driving signal to the panel unit 103, so that the panel unit 103 displays an image specified by the input signal.
The panel unit 103 includes a thin-film-transistor (TFT, hereafter) 1030, a capacitor 1031 and a liquid crystal unit 1032, wherein the capacitor 1031 is electrically coupled with the source S of the TFT 1030, the liquid crystal unit 1032 is electrically coupled with the source S of the TFT 1030, the gate G of the TFT 1030 is electrically coupled with the column decoder 102 and the drain D of the TFT 1030 is electrically coupled with the row decoder 101. The TFT 1030 decides whether or not to deliver an analog driving signal output from the row decoder 101 to the capacitor 1031 and the liquid crystal unit 1032 according to a switching signal output from the column decoder 102. Once the voltage level of the switching signal output from the column decoder 102 makes the voltage difference Vgs between the gate G and the source S of the TFT 1030 greater than a threshold voltage Vt (i. e. Vgs>Vt), a conductive path is established between the source S and the drain D of the TFT 1030. Moreover, the analog driving signal output from the row decoder 101 is able to reach the source S via the drain D of the TFT 1030 to charge the capacitor 1031 and make the liquid crystal unit 1032 luminant to display an image specified by the input signal.
The above-mentioned TFT 1030 with the driving circuit of the row decoder 101 together can be considered as a conventional driving apparatus applied to an LCD system 100. FIG. 2 is a circuit diagram of a conventional driving apparatus 200 applied to the LCD system 100. Referring to FIG. 2, a conventional driving apparatus 200 includes a driving circuit 1010 and a TFT 1030. The driving circuit 1010 is used for converting an input signal input_voltage into an analog driving signal. The gate of the TFT 1030 is controlled by a switching signal TFT_open_sig. When the path between the source S and the drain D of the TFT 1030 is turned on, the analog driving signal is output to the source S via the drain D of the TFT 1030 to charge the capacitor 1031 and make the liquid crystal unit 1032 luminant to display an image specified by the input signal.
However, when the rising speed and the falling speed of the above-mentioned switching signal TFT_open_sig are not ideal as expected, as a result, the analog driving signal may overwrite the image produced by the preceding analog driving signal of the liquid crystal unit 1032. Thus, most conventional driving apparatuses would employ an additional control switch at the output terminal of the driving circuit 1010 to avoid the above-described problem.
FIG. 3 is a circuit diagram of another conventional driving apparatus 300 applied to the LCD system 100 and FIG. 4 is a signal waveform diagram of the conventional driving apparatus 300. Referring to FIGS. 3 and 4, a conventional driving apparatus 300 includes a driving circuit 1010, a control switch 301 and a TFT 1030, wherein the control switch 301 is electrically coupled with the driving circuit 1010 and the TFT 1030, and the control switch 301 is a part of the row decoder 101 (referring to FIG. 1). The driving circuit 1010 is used for converting an input signal input_voltage into an analog driving signal output_sig. The gate G of the TFT 1030 receives a switching signal TFT_open_sig. When the TFT 1030 is turned on by the switching signal TFT_open_sig, the path between the drain D and the source S of the TFT 1030 is conductive, but a control signal control_sig blocks the control switch 301 to be turned on, which ensures the analog driving signal output from the driving circuit 1010 does not wrongfully overwrite the image produced by the preceding analog driving signal of the liquid crystal unit 1032 (as shown at time t1 in FIG. 4). After that, when the control switch 301 is turned on by the control signal control_sig, the path between both terminals of in_end and out_end of the control switch 301 is conductive, so that the analog driving signal output_sig output from the driving circuit 1010 is sent to the capacitor 1031 and the liquid crystal unit 1032 and the analog driving signal output_sig is able thereby to charge the capacitor 1031 and make the liquid crystal unit 1032 display the expected image specified by the input signal (as shown at time t2 in FIG. 4). Then, when the control switch 301 is turned off, the analog driving signal output_sig output from the driving circuit 1010 would maintain at a fixed output voltage level (as shown at time t3 in FIG. 4). Furthermore, the TFT 1030 is turned off, the analog driving signal output_sig output from the driving circuit 1010 would maintain at a fixed output voltage level (as shown at time t4 in FIG. 4). Finally, when the control switch 301 is turned on again, the level of the analog driving signal output_sig would fall to a low level (as shown at time t5 in FIG. 4).
Although the above-described driving apparatus is able to avoid the problem that the analog driving signal would overwrite the image produced by the preceding analog driving signal of the liquid crystal unit however, the driving apparatus may produce a spike current with a surging peak at the moment the control switch is turned on, and the spike current would flow in to and out from the chips and the panel of the LCD system. The spike current not only makes the chips and the panel of the LCD system generate larger power consumption and degrades heat dissipation performance, but also further damage the panel of the chips of the LCD system.
Confronting the above-described problem, lots of panel manufactures are eager to develop a driving apparatus capable of reducing spike current and the method thereof to be applied to an LCD system, so that the panel and the chips of an LCD system have longer life time, lower electricity consumption and better heat dissipation performance.